Electronic circuits such as low current crystal oscillators which produce an output frequency signal are used in numerous types of electronic devices. The output signal produced by an oscillator circuit can be used for example as a reference clock signal in an integrated circuit (IC) or other type of electronic circuitry. During the manufacture of an IC or other device incorporating such an oscillator circuit, it is beneficial to test the oscillator circuit to determine if the circuit is operational and producing the required output frequency signal. In some applications (e.g., time keeping circuits, etc.), it may be beneficial to monitor the performance of the frequency generating circuit (e.g., oscillator circuit) on a periodic basis in order to guarantee that the frequency has not changed. This periodic testing is highly beneficial in multi-stage frequency generating circuits in which anyone of the multiple stages can go bad. Such testing helps guarantee that the oscillator circuit is functioning properly.
Prior art approaches for testing such frequency generating circuits although helpful have either required too long to perform or have been limited by the working temperature range requirements of the IC or circuitry under test. Therefore, a need exists for a method and apparatus which can provide a frequency test which can overcome the above mentioned problems.